1. Field of the Invention
The present invention relates to a receiving apparatus and a receiving method which are suitable for adaptively predicting the transmission characteristic in case where OFDM (Orthogonal Frequency Division Multiplex) packet communication is executed under a fast mobile environment, a program which achieves the receiving apparatus and method, and a computer readable information recording medium which has the program recorded thereon.
2. Description of the Related Art
Recently, the quick spreading of the Internet or the like is contributing to the construction of environments under which a vast amount of information, such as multimedia information, can exchanged anytime and anywhere. Demands for mobile computing to ensure transmission of such a vast amount of information under a mobile environment using portable telephones and PHS (Personal Handyphone Systems) as well as via cable networks.
In this respect, studies are being made on broad-band wireless systems which stand comparison with cable networks and can transmit a large amount of multimedia information. Efforts are being made to realize the standardization of broad-band communication, such as IEEE 802.11a, ETSI-BRAN and ARIB-MMAC, and wireless systems which use the 5 GHz band are actively studied. Those systems employ the OFDM transmission system, one of multi-carrier transmission systems, and have achieved a transmission rate of several tens of Mbps.
In the OFDM transmission system, a sender performs serial-parallel conversion on a signal to be transmitted, performs inverse fast Fourier transformation (IFFT) on the converted signal and then performs parallel-serial conversion on the resultant signal before transmission. A receiver side performs serial-parallel conversion on the transmitted signal, performs fast Fourier transformation (FFT) on the converted signal and then performs parallel-serial conversion on the resultant signal to acquire a transmission signal.
In those systems, the moving speed of each mobile terminal is assumed to be relatively slow, such as a quasi-stationary state or a stationary state.
However, there are increasing demands that users who are moving fast by cars or the like can be provided with wireless systems having a similar transmission capability. To realize an ITS (Intelligent Transport Systems), particularly, the realization of such wireless systems is essential.
Direct adaptation of the conventional OFDM packet communication to a mobile environment however cause an amplitude phase variation in a reception signal due to multipath fading. This is originated from a change in transmission characteristic with the movement of the mobile terminal and the non-negligible influence of the Doppler effect.
In case of using the impulse response, various schemes have been proposed so far to compensate for reception signals by, for example, predicting the transmission characteristic by averaging the time series of impulse responses along the time axis for each sub-carrier (carrier frequency) of the OFDM transmission or obtaining a weighted mean using a forget coefficient.
It is however known that those schemes may have a difficulty in adequately predicting the transmission characteristic when the Doppler frequency is high at a specific sub-carrier which has been affected by the frequency selectivity fading and the signal amplitude phase varies significantly.